JP 2014-99535 A discloses a semiconductor device having a HEMT (High Electron Mobility Transistor) and a temperature sensor. In this semiconductor device, a semiconductor substrate (nitride semiconductor substrate) in which the HEMT is formed and a semiconductor substrate (silicon substrate) in which the temperature sensor is formed are connected to a common lead frame. Since a strong current flows in the HEMT, the HEMT generates heat during operation. Since this semiconductor device has a temperature sensor, the HEMT can be controlled according to the temperature detected by the temperature sensor.